A study on diurnal fluctuation of blood-aqueous barrier permeability to plasma proteins

The diurnal change of blood-aqueous barrier permeability to protein molecules was investigated in 20 eyes of 10 normal volunteers. Simultaneous determinations of aqueous flow rate and the coefficient of entry into the anterior chamber (k(in)) for plasma protein were performed at different times of the day: (a) 0800 to 1100 hr; (b) 1900 to 2200 hr of the same day; (c) 0800 to 1100 hr of the next day; (d) 1400 to 1700 hr 1 week later; and (e) 0200 to 0500 hr of the following morning. Aqueous flow rate was determined by fluorophotometry and k(in) was calculated for each period from flow rate, plasma protein concentration, anterior chamber volume and aqueous protein concentration measured with a laser flare-cell meter. Calculated values for k(in) did not fluctuate significantly among the periods, and there were no significant changes in anterior chamber volume or plasma protein concentration. Aqueous protein concentration and flow rate showed diurnal fluctuations, the patterns of which inversely corresponded to each other. It was concluded that permeability of the blood-aqueous barrier to protein remains fairly stable over a 24-hr period and the diurnal variation of aqueous protein concentration is mostly attributable to that of aqueous flow rate.